The Steel Guitar Forum

I drove to Houston yesterday and picked up a Mesa Boogie Studio Preamp.....
Spent about four hours tinkering with the Mesa Boogie yesterday. First impression: It needs a new set of matched tubes. I'm going to call monday and talk to Eurotubes. He has different sets of tubes for different styles. The preamp uses 5 12AX7 tubes. He sells JJ/Tesla. Anyway, I want the best set of tubes for a clean tone. This guy will send me a matched set that is specifically selected for the cleanest tone.

This still is one of the best sounding preamps I've ever heard. It is pretty easy to overdrive the input with BL710s, so you have to pay close attention to gain structure.

I've got the Lexicon PCM 60 hooked up to it for reverb. This sounds really lush and full through headphones. I've got a couple of different rack mount delay units that I'm going to try today with the Lexicon. (The PCM 60 does reverb only...most excellent reverb!)

I'm not using the graphic EQ at the moment. I've been using the following settings: Bass 8, Treble 3, Middle 4. I'll probably mess around with the Graphic EQ today.

At this point I'm running it into a Mackie 8 buss board and listening with some AKG headphones. The board is set flat with eq off.

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Steve Stallings
Bremond, Texas
Emmmons/Mullen/Remington
Evans

Replacing the first 12ax7 with a 12at7 will give you more clean headroom.It is easy to try out since the tubes don`t require re-biasing.

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Olli Haavisto
Polar steeler
Finland

I understand why matched tubes are important in a power amp, which is essentially a balanced "push-pull" arrangement, but why would you want them in a preamp? Preamp circuits are like a serial chain. The output of one feeds into the next. Each stage has different bias and gain characteristics. What effect are you trying to get by using "matched" tubes?

I change a preamp tube if it blows or becomes microphonic. Other than that, I don't bother. Good tubes sound good until they die, IMHO, and that really doesn't happen very often.

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<small><img align=right src="http://b0b.com/b0b.gif" width="64" height="64">Bobby Lee - email: quasar@b0b.com - gigs - CDs
Sierra Session 12 (E9), Williams 400X (Emaj9, D6), Sierra Olympic 12 (F Diatonic) Sierra Laptop 8 (D13), Fender Stringmaster (E13, A6)

Bob...
I guess you are right. I was thinking more along the lines of when I replaced the power tubes in my PV. From what I understand from Bob at Eurotube, he individually tests tubes to try to match their characteristics to your use.

<SMALL>For a very clean sound I would use a pair of the JJ ECC83S tubes that are matched and graded with a lower transconductance around the mid to high 70's. This will give you good headroom</SMALL>

This is a comment from Bob at eurotubes in reply to my question about retubing the preamp. I didn't quite understand the reference to a pair of tubes, because the preamp uses five tubes.

I have been told by several folks to replace the first tube with a 12 AT7 to achieve better headroom. Since tubes are cheap, I'll at least give it a try.

One other question. I can't get the reverb to work on this. What kind of foot switch should work?


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Steve Stallings
Bremond, Texas
Emmmons/Mullen/Remington
Evans

Steve,
I haven't hooked mine pre-amp up for quite some time but I don't remember doing anything other than turning the reverb dial up so I am not much help here but I can say that the reverb sound ain't much on this pre-amp, for emergency use only IMO, so you are not missing much if it's not working.

I use the Lawrence 710 pickups as well and what I did to keep the first tube from distorting was to install the same set of resistors that are found in the #2 input of a Fender tube amp, which cuts the gain in half. Works great and cost me about twenty cents for two 68K resistors.

Steve,

Call Tim at Mesa to get a tube chart for the pre-amp (707-778-6565). This will tell you the function of each (probably two per channel and one reverb driver). Different brands of tubes have different tonal characteristics, and matching is not necessary in pre-amp tubes.

My Palmer-Amp (german product with 15" EV-speaker) has
2 6550 for the power-amp (100 Watt) and
2 ECC 81 (or 12 AT7)
1 ECC 82 (or 12 AU7)
2 ECC 83 (or 12 AX7) for the preamp.
Very good for clean- or blues-sounds.

Horst

I have a set of schematics for the preamp. If you're interested, let me know, and I can probably scan them in and send them to you.

Michael....
Thanks, but Mesa Boogie emailed me a schematic and the manual.

I did a web search looking for info on Paul Franklin and Michael Johnson setups with their Mesa Boogies. No luck at all... Both of them are using this preamp in the studio. I'm curious if theirs have been modified or are stock. I'd also like to find out what other goodies they have in the rack

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Steve Stallings
Bremond, Texas
Emmmons/Mullen/Remington
Evans

As far as I know, Paul uses a standard Mesa Boogie Studio-preamp in the studio, and uses one channel dry and one wet. The dry for recording, the other one for monitoring. He goes trough a mosfet power-amp into two Marrs cabinets. As far as I understood. If I'm wrong, Paul, please fill me in
Thanks,
Johan www.steeljj.com

i do not use a rack but i do use amesa boogie heart breaker amp w/mpx 100 lexicon this is a great steel amp unfortunatley its being discountinued because of low rock demand and its not been discovered by steel players this amp was made of a copy like a fender twin this amp was about 1700.00 close out price is 1200.00 or less beleive me try youll like it

Paul has stated previously on the Forum (a long time ago) that his Studio Preamp is unmodified.

Another thing to keep in mind about preamp tubes: 12AX7 and 12AT7 tubes are actually two tubes in one. Each "side" of them has its own supporting network of resistors and capacitors that affect the bias and gain characteristics.

It's interesting to follow the signal path on the schematic, to see how the two sides of a tube differ. If you replace the "first" tube with a 12AT7, you are actually having an effect on two stages of amplification. Be aware of what you are doing!

As I recall, the 12AT7 expects a higher signal level and amplifies it less than a 12AX7 (given the same external components). This applies to both sides of the tube. Read your schematic!

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<small><img align=right src="http://b0b.com/b0b.gif" width="64" height="64">Bobby Lee - email: quasar@b0b.com - gigs - CDs
Sierra Session 12 (E9), Williams 400X (Emaj9, D6), Sierra Olympic 12 (F Diatonic) Sierra Laptop 8 (D13), Fender Stringmaster (E13, A6)

I must admit that I know nothing about electronics, however; I am also using L-710 pick-ups. With my G.D.Walker S.S.Pre-Amp, I must back off on the Treble to at least 9:00, and the Presence to at least 10:00. This seems to be an extreme cut for the EQ! I dug out my Goodrich Mod.6a Super Sustain Match Box, and when I put it in line, all of my EQ went back to what I consider normal settings of Treble 11:00, and Presence 12:00. This additon does not prove necessary in a Nashville 1000 amp., and to the contrary; it seems to be harmful to the overall sound! Just a suggestion worth trying.(I mean the Match Box) Thanks, Big John